Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction

Area of Science:

• Chemical Physics
• Molecular Dynamics
• Spectroscopy

Background:

• Understanding molecular dynamics in excited states requires observing both electronic and nuclear motion.
• Simultaneously tracking these motions independently in a single experiment is a significant challenge.

Purpose of the Study:

• To demonstrate a method for simultaneously observing electronic and nuclear dynamics in photoexcited molecules.
• To disentangle and study the interplay between electronic state changes and nuclear structural changes.

Main Methods:

• Utilizing ultrafast electron diffraction (UED) for simultaneous observation.
• Employing small-angle inelastic scattering to monitor electronic state changes (S₁→S₀ internal conversion).
• Using large-angle elastic diffraction to track nuclear structural changes (ring puckering).

Main Results:

• UED successfully recorded both electronic and nuclear dynamics in isolated pyridine molecules.
• Electronic transitions were observed via transient signals in inelastic scattering.
• Nuclear structural changes, specifically ring puckering, were monitored through elastic diffraction.

Conclusions:

• Ultrafast electron diffraction provides a powerful tool for simultaneously studying electronic and nuclear dynamics.
• The experiment revealed the interplay between electronic internal conversion and nuclear motion in pyridine.
• This approach offers a clear view of complex molecular processes in excited states.